Vacuum pump apparatus



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United States Patent Office 3,317,122 Patented May 2, 1967 3,317,122 VACUUM PUMP APPARATUS Werner G. Bachler, Cologne, Germany, assignor to Leybold Holding AG, a Swiss joint-stock company Filed July 6, 1965, Ser. No. 469,662 16 Claims. (Cl. 230-401) This invention relates generally to vacuum pump apparatus and more particularly to diffusion vacuum pump apparatus.

Ultimate pressure is an extremely important consideration in many high vacuum applications. This is the lowest pressure attainable in a given vacuum system. Factors limiting ultimate pressure in diffusion vacuum pump systems are the high vapor pressure components present in the pumping fluid (typically oil) of the diffusion pump. During the pumping process these components, which exist as original impurities, pumping fluid decomposition products, etc., diffuse from the pump enclosure into the vacuum chamber to greatly limit the ultimate vacuum attainable. The problem persists even when pure, carefully distilled pumping fluids are used.

Apparatus for substantially reducing this effect in diffusion vacuum pumps was disclosed by H, G. Noller, G. Reich, and W. Bachler in the 1957 Vacuum Technology Transactions, pages 6l2. The test results presented in this paper indicated that elimination of cooling from the lower wall portion of a conventional multi-jet diffusion pump would substantially improve the ultimate pressure attainable in a given system. The improved performance was attributed to a degassing effect which occurs on the pumping fluid. As the vapor stream from the bottom jet assembly nozzle strikes the hot pump wall volatile components are driven out of the pumping fluid and removed as vapor from the pump housing by an associated mechanical forepump. The result is a pumping fluid with a significantly reduced content of volatile components which tend to limit ultimate pressure.

Further experiments have shown, however, that a complete purification of the diffusion pumping fluid is not achieved with this method. Although reduced, a quantity of volatile components remains in the pumping fluid and continues to limit the ultimate pressure attainable in the system.

The object of this invention, therefore, is to provide a diffusion vacuum pump apparatus which will provide improved ultimate system pressures.

One feature of this invention is the provision in a diffusion vacuum pump apparatus of a device for heating the pumps exhaust tubulation so as to inhibit condensation therein of vapor expelled during operation of the pump.

Another feature of this invention is the provision of a diffusion vacuum pump apparatus of the above featured type wherein the heating device is adapted to heat the entire length of the exhaust tubulation between its most elevated portion and the diffusion pump exhaust port thereby inhibiting vapor condensation in all portions of the exhaust tubulation wherein the condensation can return to the pump housing under the influence of gravity.

Another efature of this invention is the provision of a diffusion vacuum pump apparatus of the above featured types wherein the heating device is an electrical heating coil which encircles the diffusion pumps exhaust tubulation.

Another feature of this invention is the provision of a diffusion vacuum pump apparatus of the above featured types wherein only that portion of the pumps wall Which lies adjacent the upper stages of a multi-stage jet assembly is cooled thereby providing a warm surface which intercepts and induces degassing of the pumping fluid vapor emanating from the pumps bottom stage.

Another feature of this invention is the provision of a diffusion vacuum pump apparatus of the above featured types including a mechanical forepump having an inlet port connected to the diffusion vacuum pump exhaust tubulation.

These and other objects and features of the present invention will become apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein.

FIG. 1 is a drawing, partly in cross section, of a preferred embodiment of the present invention; and

FIG. 2 is a plot of system pressure versus exhaust tubulation temperature illustrating the improvement in ultimate system pressure attainable with the present invention.

The diffusion pump 11 has an inlet port 12 connected for gas communication with the evacuable chamber 13 by the mating pair of flanges 14. The exhaust port 15 in the lower portion of the diffusion pump housing 16 is connected for gas communication with one end of the exhaust tubulation 17. The other end of the exhaust tubulation 17 is connected by the mating flanges 18 to the inlet port 20 of the mechanical vacuum pump 19.

Enclosed within the pump housing 16 is a conventional multi-jet assembly 21. A hollow cooling coil 22 surrounds and is in intimate contact with the outer surface of the pump housing 16. The coil 22 extends from a position adjacent the top nozzle 23 of a jet assembly 21 to a position adjacent bottom nozzle 24 and is adapted for connection to a suitable source of cooling fluid (not shown).

The exhaust tubulation 17 includes the upwardly curved lower portion 26, the vertical middle portion 27 and the inverted, U-shaped upper portion 28. The lower portion 26 is attached permanently by, for example, brazing to the pump housing 16 and to one end of the middle portion 27 by the mating pair of flanges 29. The other end of the middle portion 27 is connected by the mating pair of flanges 31 to the upper portion 28 which is in turn connected to the inlet port 20 of the mechanical vacuum pump 19.

The electrical heating coil 33 encircles the exhaust tubulation 1 7 and is adapted for connection to a suitable source of electrical power (not shown). The heating coil 33 extends from a position closely adjacent the exhaust port 15 to a position surrounding the most elevated portion of the exhaust tubulation 17.

The diffusion pump 11 ope-rates in the conventional manner to evacuate the vacuum chamber 13. A pumping fluid, for example oil, is evaporated in the pumps boiler and the resulting vapor directed at supersonic velocity through the nozzles of the jet assembly 21. As the high speed vapor stream passes between the jet assembly 21 and the inner surface of the pump housing 16, it accepts by diffusion gas molecules from the vacuum chamber 13. The gas molecules are compressed into the higher pressure region in the lower portion of the pump adjacent the exhaust port 15. The gas molecules are then pumped through the exhaust tubulation 17 by the mechanical vacuum pump 19 and expelled into the atmosphere through the outlet 40. The hot pumping fluid vapor directed against the inner surface of the pump housing 16 is condensed thereon as a result of the cooling produced by the cooling coils 2-2. This condensate flows down the inner surface of the pump housing 16 and returns to the pump boiler for reheating and re-evaporation.

As fully described in the above noted technical paper, the provision of cooling coils 22 which terminate above the level of the bottom nozzle 24 substantially improves the pressure performance of a given pump. As the vapor stream from the bottom nozzle 24 strikes the uncooled portion of the pump housing 16 only the non-volatile content is condensed. The volatile components remain in the vapor state and are removed by the mechanical pump 19. Thus, a degassing of the pumping fluid occurs and lower ultimate pressures can be attained in the vacuum chamber 13.

However, as mentioned previously, this degassing does not remove all the volatile content of the pumping fluid. A significant portion of the vapor pumped out of the pump housing 116 will condense on the inner surface of the exhaust tubulation 17 which, in conventional vacuum apparatus, operates at about room temperature. This volatile condensate will flow under the influence of gravity down the inner surface of the exhaust tubulation 17 and return to the boiler portion of the diffusion pump 11.

Thus, a final elimination of the pumping fluids high vapor pressure constituents is prevented.

The heating coils 33 of the present invention overcome this problem. When energized these coils function to warm the exhaust tubulation 17, preferably to a temperature above 70 C., and thereby prevent condensation of the expelled vapor. Accordingly, substantially all the vapor pumped through the exhaust port will pass entirely through the tubulation 17 and be expelled into the atmosphere by the mechanical forepump 19. Heating is preferably provided for the entire exhaust tubulation length which lies between the most elevated portion thereof and the exhaust port 15. This is because any liquid produced by vapor condensation in this portion of the exhaust tubulation '17 can re-enter the diffusion pump .11 under the influence of gravity.

The effectiveness of the heating coil 33 is illustrated by FIG. 2 which diagrams the pressure performance of a given diffusion pump apparatus operated in accordance with the present invention. Ultimate pressure in Torr within the vacuum chamber 13 is plotted on the vertical axis and temperature (in degrees centigrade), of the heated portion of the exhaust tubulation 17 is plotted on the horizontal axis. As shown, an ultimate pressure of approximately 10" torr was obtained in the chamber 13 with the exhaust tubulation 17 operated at approximately 10 C. However, the ultimate system pressure continually improves with increasing temperature of the exhaust tubulation 17 until an ultimate pressure of approximately 1O- torr is attained at an exhaust tubulation temperature of approximately 90 C.

Although the particular embodiment shown and described is preferred, other configurations can also prove effective. For example, only the exhaust tubulation 17 can be formed in any desired configuration or from any desired number of individual sections. Similarly, heating mechanisms other than electrical heating coils can be utilized to produce heating of the exhaust tubulation. It is therefore to be understood that within the scope of the attached claims the invention can be practiced otherwise than as specifically described.

What is claimed is:

1. A vacuum pump apparatus comprising a ditfusion vacuum pump having a pump housing enclosing a pumping mechanism, said pump housing having an inlet port adapted for connection with a chamber to be evacuated, said pump housing also having an exhaust port adapted to allow expulsion from said pump housing of the gases pumped by said pumping mechanism, an exhaust tubulation attached to said pump housing and communicating with said exhaust port so as to receive gas and vapor expelled therefrom, and heating means adapted to heat said exhaust tubulation so as to inhibit condensation therein of vapor expelled through said exhaust port.

2. A vacuum pump apparatus according to claim 1 wherein said exhaust tubulation extends upwardly from said exhaust port and said heating means is adapted to heat the entire length of said exhaust tubulation which lies between the most elevation portion thereof and said exhaust port.

3. A vacuum pump apparatus according to claim 2 wherein said heating means encircles said exhaust tubulation.

4. A vacuum pump apparatus according to claim 3 wherein said heating means comprises an electrical heater coil.

5. A vacuum pump apparatus according to claim 1 wherein said heating means encircles said exhaust tubulation.

6. A vacuum pump apparatus according to claim 5 wherein said heating means comprises an electrical heater coil.

7. A vacuum pump apparatus according to claim 1 wherein said heating means comprises an electrical heater coil.

8. A vacuum pump apparatus according to claim 7 wherein said exhaust tubulation extends upwardly from said exhaust port and said heating means is adapted to heat the entire length of said exhaust tubulation which lies between the most elevated portion thereof and said exhaust port.

9. A vacuum pump apparatus comprising a diffusion vacuum pump having a pump housing enclosing a vertically stacked multi-nozzle jet assembly, cooling means in contact with and adapted to cool a portion of said pump housing adjacent said jet assembly, said cooling means terminating at approximately the level of the bottom nozzle of said jet assembly, said pump housing having an inlet port adapted for connection with a chamber to be evacuated and an exhaust port adapted to allow expulsion from said pump housing of the gases pumped by said jet assembly, a mechanical vacuum pump connected for gas communication with said exhaust port by an exhaust tubulation, and heating means adapted to heat said exhaust tubulation so as to inhibit condensation therein of vapor expelled through said exhaust port.

10. A vacuum pump apparatus according to claim 9 wherein said exhaust tubulation extends upwardly from said exhaust port and said heating means is adapted to heat the entire length of said exhaust tubulation which lies between the most elevated portion thereof and said exhaust port.

'11. A vacuum pump apparatus according to claim 10 wherein said heating means encircles said exhaust tubulation.

12. A vacuum pump apparatus according to claim 11 wherein said heating means comprises an electrical heater coil.

13. A vacuum pump apparatus according to claim 9 wherein said heating means encircles said exhaust tubulation.

14. A vacuum pump apparatus according to claim 13 wherein said heating means comprises an electrical heater coil.

15. A vacuum pump apparatus according to claim 9 wherein said heating means comprises an electrical heater coil.

16. A vacuum pump apparatus according to claim 15 wherein said exhaust tubulation extends upwardly from said exhaust port and said heating means is adapted to heat the entire length of said exhaust tubulation which lies between the uppermost portion thereof and said exhaust port.

References Cited by the Examiner UNITED STATES PATENTS 2,630,266 3/1953 Lawance 230-101 3,141,606 7/1964 Landfors 230-401 3,273,787 9/1966 Noller et al. 230101 DONLEY J. STOCKING, Primary Examiner. w. J. KRAUSS Assistant Examiner. 

1. A VACUUM PUMP APPARATUS COMPRISING A DIFFUSION VACUUM PUMP HAVING A PUMP HOUSING ENCLOSING A PUMPING MECHANISM, SAID PUMP HOUSING HAVING AN INLET PORT ADAPTED FOR CONNECTION WITH A CHAMBER TO BE EVACUATED, SAID PUMP HOUSING ALSO HAVING AN EXHAUST PORT ADAPTED TO ALLOW EXPULSION FROM SAID PUMP HOUSING OF THE GASES PUMPED BY SAID PUMPING MECHANISM, AN EXHAUST TUBULATION ATTACHED TO SAID PUMP HOUSING AND COMMUNICATING WITH SAID EXHAUST PORT SO AS TO RECEIVE GAS AND VAPOR 